ECMO - Extracorporeal Membrane Oxygenation Cannulation Techniques and Strategies Questions and Answers — Questions and Answers
Question 1: A patient on Veno-Arterial (VA) ECMO with femoral artery cannulation develops signs of limb ischemia, including coolness and pallor in the cannulated leg. Which of the following is the most appropriate immediate intervention?
- Increase the ECMO pump flow to improve perfusion.
- Administer a bolus of an anticoagulant.
- Place a distal perfusion cannula (DPC) in the ipsilateral femoral artery. (Correct answer)
- Elevate the affected limb above the level of the heart.
Correct answer: Place a distal perfusion cannula (DPC) in the ipsilateral femoral artery.
Femoral artery cannulation for VA ECMO can obstruct antegrade blood flow, leading to limb ischemia. A distal perfusion cannula (DPC) is inserted antegrade into the artery distal to the main ECMO cannula to provide oxygenated blood flow to the limb, directly addressing the cause of the ischemia.
Question 2: In a standard femoro-jugular Veno-Venous (VV) ECMO configuration, what is the primary purpose of ensuring adequate distance (e.g., >15 cm) between the tips of the drainage and reinfusion cannulas?
- To prevent cannula migration and dislodgement.
- To minimize the risk of right ventricular rupture.
- To reduce the risk of venous thrombosis.
- To minimize recirculation of oxygenated blood. (Correct answer)
Correct answer: To minimize recirculation of oxygenated blood.
Recirculation occurs when freshly oxygenated blood returned via the reinfusion (jugular) cannula is immediately withdrawn by the drainage (femoral) cannula, reducing the efficiency of gas exchange. Maintaining sufficient distance between the cannula tips ensures that the oxygenated blood can mix with the patient's venous blood and travel to the right heart before being potentially withdrawn by the drainage cannula.
Question 3: Which of the following is a primary advantage of using a central cannulation strategy (e.g., aortic and right atrial cannulation) for VA ECMO compared to a peripheral (femoral) strategy?
- It can be performed more quickly at the bedside in an emergency.
- It is associated with a lower risk of bleeding complications.
- It provides antegrade aortic flow, reducing the risk of differential hypoxia. (Correct answer)
- It carries a lower risk of stroke and neurological complications.
Correct answer: It provides antegrade aortic flow, reducing the risk of differential hypoxia.
Central VA ECMO returns oxygenated blood directly to the ascending aorta, ensuring it travels antegrade to the coronary arteries and the great vessels supplying the brain. This avoids differential hypoxia (Harlequin syndrome), where the upper body receives poorly oxygenated blood from the native heart while the lower body is well-perfused by the ECMO circuit.
Question 4: A 35-year-old patient with severe ARDS is being cannulated for VV ECMO. The team opts for a dual-lumen single cannula to be inserted via the right internal jugular vein. Which imaging modality is crucial for confirming the optimal placement of this type of cannula?
- Chest X-ray
- Computed Tomography (CT) scan
- Echocardiography (TEE or TTE) (Correct answer)
- Fluoroscopy
Correct answer: Echocardiography (TEE or TTE)
Dual-lumen cannulas (e.g., Avalon) have specific ports for drainage from the SVC and IVC and a reinfusion port that must be directed towards the tricuspid valve. Echocardiography is essential to visualize the cannula's position within the right atrium and ensure the reinfusion jet is correctly oriented to minimize recirculation and avoid complications like right ventricular placement.
Question 5: When selecting cannula size for a patient requiring VA ECMO, the primary goal is to choose a size that allows for:
- The easiest and quickest possible insertion.
- The lowest possible prime volume for the circuit.
- A target blood flow equivalent to a cardiac index of 2.2-2.5 L/min/m2 without causing excessive shear stress. (Correct answer)
- The longest duration of use without needing to be changed.
Correct answer: A target blood flow equivalent to a cardiac index of 2.2-2.5 L/min/m2 without causing excessive shear stress.
The fundamental goal of VA ECMO is to provide adequate circulatory support. Cannulas must be large enough to achieve a target blood flow that meets the patient's metabolic demands (typically a cardiac index of 2.2-2.5 L/min/m2), but not so large as to cause significant vascular injury or so small that high pressures lead to hemolysis from shear stress.
Question 6: A patient is placed on peripheral VA ECMO via the femoral artery and vein for cardiogenic shock. Which of the following cannulation-related complications is a direct consequence of the retrograde blood flow delivered by the arterial cannula?
- Limb ischemia in the cannulated leg.
- Deep vein thrombosis in the non-cannulated leg.
- Increased left ventricular afterload. (Correct answer)
- Recirculation between the arterial and venous cannulas.
Correct answer: Increased left ventricular afterload.
In peripheral VA ECMO, the arterial cannula returns blood into the femoral artery, creating retrograde flow up the aorta. This flow opposes the native ejection from the left ventricle, thereby increasing the pressure the LV must pump against (afterload). This can lead to LV distention, stasis, and pulmonary edema, especially in patients with poor ventricular function.
